Various types of sensors are used throughout aircraft to provide information about aircraft systems and operating conditions. Due in part to the harsh operating conditions to which aircraft are subjected, the sensors generally should be protected from these operating conditions. Examples of such harsh operating conditions are high shock, high vibration, high and low temperature extremes, humidity, wetness, dust, snow, and ice. These harsh operating conditions are further exacerbated by the high velocity at which aircraft travel. To account for these operating conditions, aircraft sensors are generally robustly constructed, often resulting in increased expense and weight. It is therefore desirable to reduce the cost and weight of such sensors without unacceptable loss in accuracy.
Additionally, many aircraft sensors have touching and/or moving parts. Contacts in the sensors that require physical connections for operation may wear out and become unreliable. Replacing these already expensive sensors results in even greater expense.
In other industries, non-contact sensors have been employed in response to some of the concerns associated with contact-based sensors. Because of factors such as those noted above, these non-contact sensors have not generally been used to replace contact-based sensors in aircraft. Instead, some prior aircraft brake wear systems have generally used visual inspection of a wear pin to determine the degree of brake wear that has occurred. Several disadvantages to visual inspection exist, including accuracy and timing of inspection. Thus, it is desirable to improve the accuracy of measurement and the timing of inspection.